ANATOMY AND PHYSIOLOGY 



glands of other insects, opening as usual through the hypopharynx, 

 which is modified to form a spinning organ, or spinneret (Fig. 103). The 

 silk glands of Lepidoptera are a pair of long tubes, one on each side of the 

 body, but often much longer than the body and consequently convoluted. 

 Thus in the silk worm (Bombyx mori} they are from four to five times as 

 long as the body and in Tdca polyphemus, seven times as long. In the 



silk worm the convoluted glandular portion 

 of each tube (Fig. 104) opens into a dilata- 

 tion, or silk reservoir, which in turn empties 

 into a slender duct, and the two ducts ioin 





FIG. 104. Silk glands of the 

 silk worm, Bombyx mori. cd, 

 common duct; d, one of the 

 paired ducts; g, g, Filippi's After HELM. 

 glands; g/, gland proper; />, 

 thread press; r, reservoir. 



FIG. 105. Sections of silk gland of the silk worm. 

 A, radial; B, transverse, b. basement membrane; /, 

 intima; ,v, glandular cell with branched nucleus. 



into a short common duct, which passes through the tubular spinneret. 

 Two divisions of the spinning tube are distinguished: (i) a posterior 

 muscular portion, or thread- press and (2) an anterior directing tube. The 

 thread-press combines the two streams of silk fluid into one, determines 

 the form of the silken thread and arrests the emission of the thread at 

 times, besides having other functions. The silk fluid hardens rapidly 

 upon exposure to the air; about fifty per cent, of the fluid is actual silk 



